Operating agricultural vehicle such as tractors and harvesters often requires highly repetitive operations. For example, when plowing or planting a field, an operator must make repeated passes across a field. Due to the repetitive nature of the work and irregularities in the terrain, gaps and overlaps in the rows of crops can occur. This can result in damaged crops, overplanting, or reduced yield per acre. As the size of agricultural vehicles and farming implements continues to increase, precisely controlling their motion becomes more important.
Guidance systems are increasingly used for controlling agricultural and environmental management equipment and operations such as road side spraying, road salting, and snow plowing where following a previously defined route is desirable. This allows more precise control of the vehicles than is typically realized than if the vehicle is steered by a human. Many rely upon furrow followers which mechanically detect whether the vehicle is moving parallel to a previously plowed plant furrow. However, these guidance systems are most effective in flat terrain and when detecting furrows plowed in a straight line. Additionally, many of these systems require factory installation and are too expensive or inconvenient to facilitate after market installation.
A component for controlling the steering mechanism of the vehicle is used to control the movement of the vehicle in a desired direction. Thus, the guidance system generates a steering command which is implemented by the component which controls the steering mechanism. Often, the controlling component is directly coupled with and manipulates hydraulic pumps which comprise the power steering system of the vehicle. Other controlling components manipulate the steering wheel of the vehicle.
FIG. 5 shows a side view of an exemplary prior art motor mount 500. In FIG. 5, a electric motor 510 is coupled with a thrust bearing 511. A shaft 520 coupled with motor 510 passes through thrust bearing 511 and is coupled with wheel 521. Thrust bearing 511 is coupled with a back plate 540 via a screw 512 which defines a point of rotation for thrust bearing 511. A screw (not shown) couples spring 590 with back plate 540 which is in turn coupled with, for example, the steering column of the vehicle being controlled. A lever 550 is coupled with back plate 540 via screw which defines a point of rotation for lever 550. A screw 552 extends from lever 550 and overlies electric motor 510.
FIG. 5 shows motor mount 500 in an engaged position in which wheel 521 contacts steering wheel 560. To engage wheel 521 with steering wheel 560, lever 550 is pulled in the direction typically shown as arrow 570. As a result, lever 550 rotates around screw 551, thus causing screw 552 to move over the back of electric motor 510 and engage a groove 513 cut into the housing of electric motor 510. This in turn causes thrust bearing 511 to rotate around screw 512, which results in wheel 521 moving in the direction typically shown as arrow 580 and compressing spring 590. To disengage wheel 521 from steering wheel 560, lever 550 is moved in the opposite direction to disengage screw 552 from groove 513.
Motor mount 500 is problematic in that after repeated use, groove 513 becomes worn such that it becomes difficult for screw 552 to remain engaged in groove 513. As a result, wheel 521 can unintentionally become engaged with steering wheel 560. For example, if a user is manually steering a vehicle and hits a bump, wheel 521 can become engaged with steering wheel 560. This can be especially dangerous if the guidance system is generating steering commands at that moment as the vehicle may be steered in an un-intended direction as a result.
Another drawback of motor mount 500 is that screw 512 uses a lock nut having a nylon insert to maintain a desired amount of tightness. Over time, the nylon insert becomes worn, thus allowing thrust bearing 511 to move out of plane. This results in reduced precision for the guidance system because when electric motor implements steering commands, torque induced by the turning of motor 510 causes the out of plane movement. As a result, friction between wheel 521 and steering wheel 560 is lost which can result in a loss of steering precision.
Additionally, adjustment of the torque applied to screw 512 during assembly necessitates some degree of skill on the part of the assembler. For example, if screw 512 is tightened too much, it becomes too difficult to rotate thrust bearing 511 around the axis defined by screw 512. However, not tightening screw 512 enough introduces a loss of precision as described above. This is further complicated by the nylon inserts themselves which typically exhibit a wide range of tolerance with respect to the amount of torque that can be applied. As a result, the person assembling motor mount 500 has to learn by experience how much torque to apply during assembly.